Berlin Air 90 is total garbage, a prizm even is a bad skimmer on a 55 gallon. IMO, an AquaC remora is about as small as you should go. Your already spending a fair bit on the canister (i have a 2229, its pretty impressive for a filter). Look at this site www.rshimek.com under the reef section, theres an article on deep sand beds. I use dsb's on all my tanks that can facilite their use. Once the are function, they are bar none the best filter you can have on any tank, period. They do nitrification/denitrification, meaning your tank can have 0 ammo, 0 nitrite, 0 nitrate. They reduce the need for water changes greatly. It will actually export nutrients out of the tank in the form of nitrogen gas.
Hiding... powerheads up in the top corners, heater against the back lip at the top (horizontal) spraybar same idea. The intake for the filter is harder to hide, as its verticle (and green with a white prefilter sponge), so place it behind some live rock.
Sumps... they are cool, but its an expensive/time consuming thing to do. Lots of research. Other than that, you should have no problems.
What about fresh water tanks? Not to change the subject. :-[ ;D